We know that the SI unit of force is called Newton (symbol N), in momory of Newton. But does you know what is 1N equal to before the unit Newton is used?
We know that the bigger the force, the greater the acceleration; the larger the mass, the smaller the acceleration. That is how we get teh formula F=m*a, where "F" represents force," m" stands for mass, and "a" means acceleration. Think about the units of m and a. For mass we use kg as SI unit, and for acceleration we use m/s2. So when the product of m and a will will have the unit of kg * m/s2, and that is the unit of force. And since this looks long and complicated, we use Newton (N) instead.
Before SI unit was born, we have English system. In English system we use "pound" as unit of force. Currently, fewer and fewer countries are using the English system. And in science we never use English system to do calculations, we use SI unit all the time.